you could have several different things wrong to cause this. Batteries not charged or can't charge due to bad one, bad motor, bad control module, or bad connection in wiring in one or more places. My grandson's mx650 worked fine for a dozen or so charge cycles but then started with intermediate starting problems. The power light was red and the full light would be green but switch to low amber light and back and forth on its own with no motor response when was on low amber light. He had been running it in wet conditions a couple of times and am sure that was what caused the problem which after taking the battery panels off and examining closely found what was wrong. This problem caused the intermediate starting and stopping and also would not let batteries charge right. I moved wiring while looking at the green light and amber light and found when touching the fuses connections is when lights would change. looked at all 3 30 amp fuses and 2 of them was burnt and pitted. You could see the ark in low light at the fuse when you operated the throttle, that turned out to be a good test to see what was wrong and what caused the fuses to become pitted. I sanded the fuses and clean since they were not blown and used dielectric grease in the connection and that seems to have fixed the problem. I also used the grease in some of the other connections for good luck. The bike charges now like is supposed to and the throttle lights are ok now, no more going from green to amber when wanting power. I would say the running in wet conditions is what started the problem and washing off the bike with a hose would do the same thing.

It is the rear freewheel assembly causing the problem. if is fixable, but you have to be good with tools, the bicycle shop and the electric bike shop both said they couldn't fix it, but is is doable. 1. you need a special bmx tool that fits that back wheel, your local bike shop should have it in stock. 2. you need to remove the freewheel sprocket and disgard it along with the the bearings (make sure to unscrew the razor chain sprocket from the freewheel assembly and secure it for reuse). 3. either purchase a new freewheel sprocket for bmx wheel or remove one from a old bike (again you will a special tool for that). 4. screw the razor chair sprocket onto the new BMX sprocket (it goes on with the same 4 original screws, right over the sprockets. 5. Screw the freewheel back onto the rim now. tada its fixed.

WOW!!!WHAT A JOKE!MY KID SAVED $470 AND PURCHASED HIS MX 650 ONLY TO HAVE THE REAR FREEWHEEL BREAK THE FIRST WEEK RIDING IT.NND BY SEEING ALOT OF THE SAME PROBLEMWITH EVERYONE ELSE.RAZOR SHOULD' VE AT LEAST PUT A HEAVYDUTY ONE IN IT.OK PEOPLE LETS FIGURE IT OUT IF ANY ONE KNOWS AGOOD BEARING COMPANY,POST IT.MY KIDS BUMMED HE CANT RIDE IT

Sadly most "low end" products have these problems.
I have been an assembler for a while now and i've seen this problem too many times. The product comes made with the assumption it is not going to get put together as sturdy as many people feel it should be.
My only suggestion would be to try and use a pair of vice grips or pliers to work the screw out and replace it with you feel is more reliable. At the end of the day the company is only looking to make money so the cheaper the product they can get by with, the better it is for them.
Good luck! :)